Serial Adapters Information

Serial adapters are devices that permit interfacing between a computer bus and a serial device. Serial adapters may only include two connectors, thus allowing one device to connect to one bus. Other products may allow the bus to connect to multiple serial ports. Serial adapters allow serial connections to USB, Bluetooth, RS232, RS485 and other types of interfaces.

The following video explains the role of serial communication in networking, the need for conversion between a bus and a serial device, and details about several common serial protocols.

Video credit: Real Time Automation

Serial Protocols

Serial adapters may interface with one or several different serial protocols. The following table specifies basic information about each protocol.

Standard

RS-232

RS-422

RS-485

Mode

Single

Differential

Differential

Drivers / receivers on one line

1 / 1

1 / 10

32 / 32

Max. cable length (ft.)

50

4000

4000

Max. data rate

20 kbps

10 Mbps

35 Mbps

Max. driver output voltage

±25V

-0.25V to +6V

-7V to +12V

Table Credit: rs485.com

RS-232

RS-232 is a popular serial protocol which allows asynchronous data transfer at 9600 bits per second (bps) at 15 meters. RS-232 was once widely used in computer ports, but has since been largely replaced by universal serial bus (USB) ports due to the higher speed, lower voltage requirements, and simpler connectors in using USB. RS-232 is a single-ended signal method, meaning that the signal is generated by varying the voltage of one wire in relation to another wire's reference voltage, or ground. While more complicated differential signaling protocols allow for higher transmission speeds and longer distances, single-ended protocols are simpler and use fewer wires. Single-ended signaling is typically adequate for slower transmissions over short distances.

RS-422

The RS-422 standard specifies differential signaling, meaning that data is transmitted using two complementary signals sent on two paired wires, known as a differential pair. This results in a much higher transmission rate of up to 10 Mbps, or up to 110 kbps at 1.2 kilometers. The use of differential transmission also lessens signal interference due to ground shifts and induced noise effects incurred by sing-ended types. RS-422 also allows for a multi-drop, or "party-line" setup in which one driver controls a bus of up to 10 receivers. Like RS-232, RS-422 recommends the use of D-sub connectors.

RS-422 signaling is often used to extend RS-232 signaling, and to control remote equipment in the broadcast automation and post-production editing industries.

RS-485

RS-485 allows for the use of differential signaling to create a truly multi-point network. Multi-point networking is similar to the multi-drop capability described in the above section, except that multi-point capability allows each device to both send and receive signals at different times. RS-485 specifies baud rates of up to 35 Mbps at 100 meters up to 100 kbps at 1200 meters. It is especially useful in very long distance or extremely noisy industrial applications.

Network

Mounting Options

Serial adapters may feature one of several different mounting or form factor types:

Rack mounted devices are mounted on racks with hardware such as rail guides, flanges, or tabs. Some serial adapters may fit a standard 19" telecommunications rack.

Desktop devices sit atop a desk or fit inside a tower or other structure.

Portable adapters are designed to be moved and may have handles, wheels, or a case to facilitate this. Portable devices may be, but are not necessarily, handheld.

DIN rail products mount on a metal rail originally specified by Deutsches Institüt fur Normüng (DIN), a German national standards body. DIN rails come in a variety of widths, including 15 mm, 35 mm, and 75 mm, and may be C-shaped, G-shaped, or "top hat" shaped.

Panel mount adapters fit into a depression into a panel, so that they are flush or nearly flush with the panel front.

Printed circuit board (PCB) mounts involve attachment to an electrical enclosure, or directly to a circuit board using pins or plugs.

Connectors

The Engineering360 SpecSearch database contains information about a number of different serial adapter connector types.

DB9 and DB25 connectors are D-subminiature (D-sub) connectors with 9 or 25 pins, respectively. D-sub connectors contain two or more parallel rows of pins or sockets surrounded by a D-shaped metal shield. An image and pinout of the DB25 connector is shown above. While D-sub connectors were once among the smallest electrical components in use and regarded as technologically advanced, they have largely been supplanted by smaller connectors such as SATA, USB, and FireWire®. General usage of D-sub connectors has been in decline due to their large size and high cost, and the increasing prevalence of smaller connectors in devices such as MP3 players and mobile phones.

RJ-11 and RJ-45 connectors are two types of registered jack (RJ) devices. RJ-11 connectors have two contacts and are often used for telephone communications. RJ45 connectors feature eight contacts and are used to connect computers to local area networks (LAN) or to connect telephones with many lines.

Bayonet Neill-Concelman (BNC) connectors are quick connect devices often used with coaxial cables. BNC connectors were originally designed for military applications but are now in use in general applications. These connectors are often used in serial digital interface applications, as well as to connect radio antennas and test equipment.

References

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Related Products & Services

Serial communication products are used in industrial and commercial systems to transmit data bit-by-bit, or sequentially, over a single wire. They include serial servers, serial hubs, serial adapters, serial data converters, serial routers, and serial multiplexers.